Retina Display is a brand name developed by Apple to refer to devices and monitors that have a resolution and pixel density so high – roughly 300 or more pixels per inch that a person is unable to discern the individual pixels at a normal viewing distance.

In layman's terms, ppi refers to the number of pixels spread across the surface area of the screen. You can calculate your own ppi using calculators like this http://www.sven.de/dpi/

It’s been noted that with 20/20 vision the human eye can distinguish pixels at up to 400 ppi.

Apple's Retina Display made its debut on 2011's iPhone 4S, which featured a 960x640 pixel screen with four times the number of pixels (326 pixels per inch) as the iPhone 4.

Before you kick start, Imbibe the below mantras

If you’ve read emails on a retina display you may have noticed that some graphics look a little blurry. Standard-resolution bitmap images can look blocky on a Retina display and when scaled bigger, it might not remain smooth.

So, how do you accommodate for these higher resolution displays and create an HTML email that looks brilliant on a Retina Display?

One double-sized graphic for all recipients

In emails, you don’t have the option of serving up the higher density image only when needed so you’ll need to develop your email in a way that the
double-sized retina-friendly graphic gets served to everyone.

Create your images at a perfect 2x aspect ratio to the original size

Doing so, the integrity of the image will look as perfect as it should be after scaling, especially if the graphic contains any text.

Watch your file size

Unlike web where you can control the file size using CSS, in emails you can’t do that! With doubling of the width and height of the images, you will also end up increasing file size. Be careful!

Focus more on logos, icons and buttons

In emails, simpler graphics like logos, buttons and icons are easy to be converted to higher resolutions without making the file size humongous.

Watch out media queries for responsive email html

Doubling the size of images and then scaling them might be challenging in responsive html. To do so successfully, make sure that media queries aren’t setting a fixed size that conflicts with the way you are scaling the images.

Monks’ Verdict

The Retina display is the best screen you'll find on any device, and the difference it makes to your email viewing is dramatic.

Although on a minute observation. It's like upgrading from dot matrix printers to laser ones, or from VHS to DVD.